1. Field of the Invention
The invention is directed to an electrode and an electrocatalytic coating thereon for use in aqueous chlor-alkali solutions which provides a lower start-up and overall operating voltage.
2. Description of the Related Art
Electrodes for use in electrolytic processes have been known which have a base or core metal bearing a layer or coating of metal oxides. The core metal of the electrode may be a valve metal such as titanium, tantalum, zirconium, niobium or tungsten. Where the coating is an oxide mixture, an oxide of the core or substrate can contribute to the mixture. Such mixture can include an oxide of the substrate metal plus at least one oxide of a metal such as platinum, iridium, rhodium, palladium, ruthenium and osmium. Such electrodes are known in the art and generally referred to as “dimensionally stable”.
An inherent drawback of these coatings in a chlorine/chlorate production environment, however, is the detrimental effect on chlorine evolution potential, leading to a higher operating potential and the necessity for a voltage “break-in” period during which the anode operates at a higher potential for up to several months.
Attempts to overcome the disadvantage associated with chlorine evolution potential have been addressed in U.S. Pat. No. 4,233,340 in which there is provided an insoluble electrode having a coating containing a baked slurry of palladium oxide containing a platinum compound which can be thermally decomposed to form platinum metal. The coating contains 99 to 5 mol % palladium oxide and 1 to 95 mol % platinum metal. In U.S. Pat. No. 4,443,317 there is taught an electrode for electrolysis having a coating consisting of 40 to 90 mol % palladium oxide, 0.1 to 20 mol % platinum and 5 to 50 mol % (RuxTi1-x))2.
Therefore, it would be advantageous to provide an electrode having a coating thereon which would eliminate the necessity for a voltage “break-in” period and provide an overall lower operating potential. It would be further desirable for such an electrode and coating to prevent or eliminate an escalation in voltage following postbaking of the coating.